1. Field
Various embodiments of the present invention relate to a semiconductor design technology, and more particularly, to a semiconductor device for generating internal command signals.
2. Description of the Related Art
In general, semiconductor devices including a double data rate synchronous DRAM (DDR SDRAM) receive an external command from the outside. The external command is inputted in a form of various command signals (hereinafter, referred to as “external command signals”). The semiconductor devices perform various operations corresponding to the external command signals by decoding the external command signals. For example, a semiconductor device may perform an active operation, a precharge operation, a write operation, a read operation or the like in response to the external command signals. The external command signals inputted to the semiconductor device are an active signal, a chip select signal, a row address strobe (RAS) signal, a column address strobe (CAS) signal, a write enable signal, and the like.
FIG. 1 is a block diagram illustrating a conventional internal command signal generating circuit.
Referring to FIG. 1, the conventional internal command signal generating circuit includes a command decoding unit 110. The command decoding unit 110 receives and decodes external command signals “CST”, “ACTT”, “CAST”, “WET” and “RAST”, and generates internal command signals “ACT”, “AFACT”, “MRS”, “PCG” and “ZQC”. Here, the external command signals “CST”, “ACTT”, “CAST”, “WET” and “RAST” correspond to a chip select signal, an active signal, a column address strobe signal, a write enable signal and a row address strobe signal, respectively. In addition, the internal command signals “ACT”, “AFACT”, “MRS”, “PCG” and “ZQC” are internal command signals for activating corresponding operations. The internal command signal “ACT” is a signal for an active operation, the internal command signal “AFACT” is a signal for a refresh operation, the internal command signal “MRS” is a signal for a mode setting operation, the internal command signal “PCG” is a signal for a precharge operation, and the internal command signal “ZQC” is a signal for an impedance calibration operation of an output pad. Meanwhile, to operate semiconductor devices at a higher speed, the frequencies of clock signals applied from the outside become higher. A frequency of a clock signal determines the operating frequency of a semiconductor device